The present invention relates generally to apparatuses having a function of transmitting electric power between sprung and unsprung parts of a vehicle, and more particularly to a shock absorber having a function of transmitting electric power between sprung and unsprung parts of a vehicle.
In recent years, there have been developed various electric vehicles for environmental protection. In particular, compact electric vehicles with a short distance per charge become widely available. Some of the compact electric vehicles include an electric motor attached to a wheel assembly, to use the limited space efficiently. On the other hand, an electric brake system, which is driven by an electric motor instead of a hydraulic circuit, is under study, to reduce liquid waste of brake fluid. These vehicles need electric power supply from sprung parts (body) to unsprung electrical components, especially electric motors, near wheel assemblies. In general, electrical components and power supply are directly connected with wire in electric vehicles. In middle size electric vehicles, the strokes of suspensions are long to provide preferable ride, and the thicknesses of wires are large in accordance with large capacities of motors. In this structure, bended repeatedly, the wire may get fatigued to break. Japanese Patent Provisional Publication No. 11-18212 (JP11-18212) discloses a technique against this problem. In JP11-18212, a power supply system includes a first coil as a sprung component, and a second coil as an unsprung element. Electric power is transmitted by electromagnetic induction between the pair of the coils. In other words, a transformer is formed to transmit electric power between sprung parts to unsprung parts.